1. Field of the Invention
The present invention relates to a forward/backward gear shifting mechanism provided with a selector rod for selectively shifting a forward/backward selector included in a propulsion unit of an outboard engine.
2. Description of the Related Art
A marine propulsion machine has a propulsion unit driven by an engine and including a propeller. The propulsion unit includes a forward/backward gear. A shift rod is operated by a remote control device using an operating cable to shift the forward/backward gear to either a forward-drive position or a backward-drive position.
An outboard engine disclosed in JP 9-123996 A has a shift link connected to a remote control cable with a pin that slides along a guide groove formed in a guide attached to an exhaust guide, and a shift arm connected to the shift link with a pin and fastened to a shift rod. Shifting force is transmitted through the remote control cable extending from a remote controller, the pin and the shift link to the shift arm to the shift rod to drive the shift rod.
In this known outboard engine, the joint of the remote control cable and the pin, and the joint of the pin and the shift link are at the same position with respect to a longitudinal direction from a cable holding part at which the remote control cable is held on a bracket. Therefore, the position of the shift link is decided uniquely when a stroke for which the remote control cable needs to be moved to move the shift link is determined. Thus, there is a restriction on the position of the shift link.
An outboard engine disclosed in JP 8-91296 A is provided, to drive a shift rod in a remote control mode, with an input shift arm fastened to a shaft supported for turning on a bracket fastened to a crankcase, an output shift arm fixed to the upper end of an output shift shaft supported for turning on the crankcase, a shift link connecting the input shift arm and the output shift arm, a driving sector gear attached to the lower end of the output shift shaft, and a driven sector gear attached to the upper end of the shift rod and engaged with the driving sector gear. Operating force applied to a shift lever by an operator to change the position of the shift rod is transmitted through a Bowden cable connected to the shift lever to the input shift arm. The motion of the input shift arm is transmitted through the shift link, the output shift arm and the driving sector gear to the driven sector gear to drive the shift rod.
Each of the outboard engines described in JP 9-123996 A and JP 8-91296 A is provided with a linkage including the shift link to drive the shift rod by the operating force. In the outboard engine disclosed in JP 8-91296 A, the shift link connecting the input and the output shift arm needs to turn relative to the input and the output shift arm and hence some clearances are formed in the joints of the shift link, and the input and the output shift arm. The clearances cause a time lag between the motion of the input shift arm turned by the cable and the motion of the output shift arm moved by the shift linkage. Consequently, the relation between the operating position of the operating member and the selected position of the shift rod is not always fixed and the operator is unable to obtain a satisfactory shift feeling.
In each of the outboard engines disclosed in JP 9-123996 A and JP 8-91296 A, the shift link performs both a translating motion and a turning motion and hence a comparatively wide space must be available for the motion of the shift link. Thus, it is difficult to install the linkage in a narrow space, restrictions are placed on the arrangement of the members related with the shift link and it is difficult to arrange the associated members compactly.
In the outboard engine disclosed in JP 8-91296 A, the Bowden cable is fastened to the input shift arm. Therefore, the Bowden cable is curved and resistance against the sliding movement of the Bowden cable increases when the input shift arm is turned. Consequently, the lightness of the shifting operation is spoiled.
The outboard engine disclosed in JP 8-91296 A is provided, to operate the shift rod in a remote control mode, with the input shift arm fastened to the input shift shaft, the output shift arm fixed to the upper end of the output shift shaft, the shift link connecting the input shift arm and the output shift arm, the driving sector gear attached to the lower end of the output shift shaft, and the driven sector gear attached to the upper end of the shift rod and engaged with the driving sector gear. Operating force applied to the shift lever by the operator to operate the shift rod is transmitted through the Bowden cable connected to the shift lever to the input shift arm, and from the input shift arm through the shift link, the output shift arm, the driving sector gear and the driven sector gear to drive the shift rod. The output shift arm has a depression that receives a roller supported on the extremity of a leaf spring, and a dog for operating a limit switch to send out a neutral-indicating signal.
In the outboard engine disclosed in JP 8-91296 A, a rotational axis about which the output shift arm provided with the dog turns is on a line parallel to the moving direction of the actuator, which moves to close and open the contact of the limit switch. There is not any choice of determining the position of the limit switch, the dog having a length from the rotation axis needs to turn in a wide turning range to move the actuator properly. Thus, it is difficult to form a shifting device provided with such a limit switch in compact construction.
The leaf spring that creates a click to enable the operator to recognize the shift of the shift rod to a neutral position, and the dog for operating the limit switch are separate members. Therefore, in some cases, the detection of the shift of the shift rod to the neutral position and operator's perception of a click do not occur simultaneously.
The need to position the leaf spring so that the resilience of the leaf spring may not affect the turning motion of the output shift arm places restrictions on the placement of the leaf spring and the limit switch, making it difficult to form the forward/backward gear shifting mechanism in compact construction.
In the outboard engine disclosed in JP 8-91296 A, the Bowden cable passed through the wall of the under case has one end connected the input shift arm and the other end connected to the shift lever disposed at a distance from the outboard engine. The operating force applied by the operator to change the propulsion mode is transmitted through the Bowden cable connected to the shift lever, the input shift arm, the shift link, the output shift arm, the driving sector gear and the driven sector gear to the to the shift rod.
In the outboard engine disclosed in JP 8-91296 A, the rotational axis of the driving sector gear in mesh with the driven sector gear lies on a longitudinal straight line passing a steering axis. Therefore, the distance between the rotational axis of the input shift 14m and that of the driving sector gear is long, the input shift arm, the shift link, the output shift arm and the driving sector gear occupy a large space, and hence the outboard engine is large.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a forward/backward gear shifting mechanism for an outboard engine, capable of securing a necessary stroke of an operating cable, of increasing choices of disposing a transmission mechanism and of being lightly operated for a propulsion mode changing operation. Another object of the present invention is to increase choices of disposing a pivot shaft regardless of the position of the joint of an operating cable and a linking member.
A further object of the present invention is to provide a forward/backward gear shifting mechanism for an outboard engine, capable of producing an improved shift feel, including a compact transmission mechanism, of increasing choices of disposing the transmission mechanism, and of improving operating lightness.
A still further object of the present invention is to provide a forward/backward gear shifting mechanism for an outboard engine, capable of increasing choices of disposing a neutral-indicating switch, of being formed in compact construction, and of eliminating time lag between the detection of the shift of a shift rod to a neutral position and operator's perception of a click.
An additional object of the present invention is to provide a forward/backward gear shifting mechanism provided with a compact transmission mechanism for transmitting an operating force applied to an operating cable to a driving member for driving a shift rod, capable of being highly lightly operated, of producing an improved shift feel, and of increasing choices of disposing the transmission mechanism.